I get pain near lower back and upper buttocks while standing up after seating. No pain while walking etc... Just pain when I stand up.

Sacrum pain? If you put your hands on your hips, and touch your thumbs together, if the pain is below that it may be from sacroiliitis. This is a connection between the pelvic bones and the lower spine. It has to tighten when you go from sitting to standing. Stretching, massage, and over the counter medications like ibuprofen, can help.
See your doctor. You should let your doctor know you are having pain. He/she can examine you and possibly run tests to find out the cause.